Blood-feeding insects, such as mosquitoes, transmit deadly pathogens like malaria parasites, dengue viruses, and filarial worms to hundreds of millions of people every year. Insect repellents can be very effective in reducing vectorial capacity by blocking the contact between blood-seeking insects and humans; however, they are seldom used in disease-prone areas of Africa and Asia due to high costs and need for continuous application on skin.
N,N-Diethyl-m-toluamide (DEET) is an example of an insect repellent used in the developed world for more than sixty years. The use of DEET as an insect repellent, however, has several drawbacks. For example, DEET is a solvent capable of melting several forms of plastics, synthetic fabrics, painted and varnished surfaces (Krajick et al., Science, 313: 36, 2006). Additionally, DEET has been shown to inhibit mammalian cation channels and human acetylcholinesterase, which is also inhibited by carbamate insecticides commonly used in disease endemic areas (Corbel et al., BMC Biol, 7, 2009). These concerns are enhanced by the requirement of direct and continuous application of DEET to every part of exposed skin in concentrations that can be as high as 30-100%. Several instances of increased resistance to DEET have also been reported in flies, Anopheles albimanus, and Aedes aegypti (Reeder et al., J Econ Entomol, 94: 1584, 2001; Klun et al., J Med Entomol, 41: 418, 2004; Stanczyk et al., Proc Natl Acad Sci USA, 107: 8575, 2010). Moreover, mosquito strains with resistance to pyrethroid insecticides, the main line of defense against mosquitoes in developing countries, are spreading (Butler et al., Nature, 475: 19, 2011). The other major barrier in developing new repellents is the time and cost of development, which can take more than $30 million and several years to identify new compounds that not only repellent to insects, but are also safe for human use.
Thus, what is needed in the art are alternative compounds to DEET that can be used as insect repellents but are safe for human use, and methods of identifying such alternatives.